JPH0770099B2 - Magneto-optical recording method - Google Patents

Description

The present invention relates to an overwritable magneto-optical recording medium using a Curie point recording type magneto-optical recording medium that can be read by utilizing the magnetic force effect. Regarding the improvement of the recording method.

[Prior Art] A magneto-optical memory is known as an erasable optical memory, which enables high-density recording and non-contact recording / reproducing as compared with a magnetic recording medium using a conventional magnetic head. On the other hand, it has the disadvantage that the recorded portion must be erased once before recording (it must be magnetized in one direction) before recording.
A method of providing a recording / reproducing head and an erasing head separately,
Alternatively, a method of recording while irradiating a continuous laser beam and modulating a magnetic field applied simultaneously has been proposed.

However, these methods have the drawbacks that the device becomes bulky and the cost is high, or high-speed modulation cannot be performed.

Therefore, there has been proposed a magneto-optical recording method capable of overwriting similar to that of a magnetic recording medium by simply adding a magnetic field generating means having a simple structure to the conventional apparatus configuration. (Japanese Patent Application No. 62-20384 of the applicant of the present application (Japanese Patent Laid-Open No. 63-1
53752), Proceedings of the 34th Joint Lecture on Applied Physics (1
987) 28p-ZL-3).

In this method, an exchange-coupled two-layer structure composed of a recording layer having a low Curie temperature and a high coercive force and an initialization layer having a relatively high Curie temperature and a low coercive force as compared with the recording layer is used. A perpendicular magnetic film is used as a recording medium.

Then, when the laser intensity is modulated into “high” and “low” respectively corresponding to “1” and “0” of the recording signal on this recording medium and initialized by the initialization magnetic field, for example, as shown in FIG. The magnetization state is as shown in.

[Problems to be Solved by the Invention]

In FIG. 2, for example, a rare earth-iron group amorphous alloy thin film having the same composition as the compensating composition is considered as the recording layer and the initialization layer. Here, 4 is a domain wall (Bloch domain wall) formed on the side surface of the cylindrical magnetic domain 3 recorded in the recording layer 1,
Reference numeral 5 denotes a domain wall (interface domain wall) formed at the boundary between the cylindrical magnetic domain and the initialization layer 2. Here, the domain wall is a transition region in which the magnetic moment gradually changes its direction, stores a certain amount of energy, and the domain wall always tries to reduce its area.

In this figure, both the Bloch domain wall and the interface domain wall try to reduce the area thereof (the area for stabilizing the magnetization of the recording magnetic domain is to be enlarged), so that both of them act to collapse the recording magnetic domain. Further, since the initializing magnetic field 6 also acts in the direction of decreasing the area of the Bloch domain wall, the recording magnetic domain becomes more unstable.

An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional example, and an object of the present invention is to provide a recording method in which the stability of recorded information is improved by controlling the location of the interface magnetic wall.

[Means for Solving the Problems]

The present invention, which can achieve the above-mentioned object, is exchange-bonded, which comprises a recording layer having a low Curie temperature and a high coercive force and an initialization layer having a relatively high Curie temperature and a low coercive force as compared with the recording layer. A magneto-optical recording medium having a two-layered perpendicular magnetization film on a substrate,
In a magneto-optical recording method that overwrites by irradiating a laser whose intensity is modulated corresponding to binary information of "1" and "0", a relatively low laser power is irradiated corresponding to "1". After that, the magnetization of the initialization layer is initialized in one direction to form a magnetization state in which an interface domain wall does not exist between the recording layer and the initialization layer, corresponding to “0”. Forming a magnetization state in which an interface domain wall exists between the recording layer and the initialization layer by unidirectionally initializing the magnetization of the initialization layer after irradiation with a relatively high laser power; , And a magneto-optical recording method.

It is a particularly preferred embodiment that the recording layer and the initializing layer are made of a rare earth-iron group amorphous alloy thin film having a composition opposite to the compensating composition.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a magnetization state according to the recording method of the present invention. In this method, the laser intensity is modulated to “low” and “high”, respectively, in response to “1” and “0” of the recording signal, and recording is performed.

After that, FIG. 1 shows the initialization by the initialization magnetic field.

In this aspect, the interface magnetic wall 5 exists in a region other than the region where the recording magnetic domain 3 is formed. Further, it is preferable to use a rare earth-iron group amorphous alloy thin film having a composition opposite to the compensation composition as the recording layer and the initialization layer. At this time, both are stable in a state where the magnetizations are antiparallel.

Also in FIG. 1, the Bloch domain wall 4 and the interface domain wall 5 try to reduce their areas, but the Bloch domain wall acts to collapse the recording magnetic domain (reduces the area for stabilizing the magnetization of the recording domain). On the other hand, the interface domain wall acts to widen the recording magnetic domain (enlarges the region that stabilizes the magnetization of the recording magnetic domain). Therefore, since the Bloch domain wall and the interface domain wall have opposite action directions, the actions are canceled each other, and the stability of the recording domain is improved.

In this case, if the energy densities of the Bloch domain wall and the interface domain wall are the same, the ratio of the action of the Bloch domain wall and the action of the interface domain wall is equal to the ratio of the reciprocal of the diameter of the recording magnetic domain to the reciprocal of the film thickness of the recording layer. Generally, since the diameter of the recording magnetic domain is larger than the film thickness, the actions of the two do not cancel each other out, and the action of the interface domain wall to widen the domain remains.

Even if a rare earth-iron group amorphous alloy thin film having the same composition as the compensating composition is used as the recording layer and the initializing layer, the magnetic domain stability is increased by forming the interface domain wall outside the recording domain. However, if the initializing magnetic field can be applied in the direction of crushing the magnetic domains, the interface magnetic domain wall cancels the action of expanding the magnetic domains, thereby further improving the recording stability.
In order to apply the initializing magnetic field in the direction to collapse the magnetic domain,
As shown in the figure, a rare earth-iron group amorphous alloy thin film having a composition opposite to the compensating composition is used as the recording layer and the initialization layer, and the magnetization of the recording domain and the magnetization of the initialization layer are antiparallel to each other. Should be

In order to completely cancel the action of the Bloch domain wall and the action of the interface domain wall, it suffices to increase the film thickness of the recording layer, but this is not practical because the recording sensitivity becomes poor. Instead, it is better to lower the energy density of the domain wall. For that purpose, a perpendicular magnetization film (Gd-Fe, Gd-Fe-Co, Gd-Co, Gd-Tb) having a small domain wall energy is provided between the recording layer and the initialization layer.
-Fe, Gd-Tb-Fe-Co, Gd-Tb-Co, etc., or in-plane magnetized film (Fe, Co, Ni or Gd-Fe, Gd- with large magnetization)
Fe-Co, Gd-Co, Gd-Tb-Fe, Gd-Tb-Fe-Co, Gd-Tb
-Co etc.) should be sandwiched between the preparations.

[Example 1] A disk-shaped substrate made of polycarbonate with pregrooves and preformatted signals engraved in a sputtering apparatus equipped with a ternary target, and a distance of 15 cm from the target.
It was set to the interval of and was rotated.

Sputtering speed of 40 from the first target in argon
Å / min., Sputtering pressure 1.5 × 10 ^-1 Pa and Si ₃ N ₄ as a protective film with a thickness of 500 Å. Next, in argon, sputter rate 100 Å / min., Sputter pressure 1.
A Tb-Fe alloy was sputtered at 5 × 10 ^-1 Pa, and a recording layer with a film thickness of 500 Å, T (Curie temperature) _L = about 130 ° C, H (coercive force) _H = about 15 KOe and Fe sublattice magnetization predominant was formed. Formed.

Next, in Argon, the sputtering rate from the third target was 100 Å / min., And the sputtering pressure was 1.5 × 10 ^-1 Pa.
o Alloy sputtered, film thickness 700Å, T _H = about 220 ° C, H _L = about 4
KOe, a Gd-Tb sublattice magnetization-dominated initialization layer with a compensation temperature of about 140 ° C was formed.

Then, in argon, the sputter rate from the first target is 40
Å / min., Sputter pressure 1.5 × 10 ^-1 Pa and Si ₃ N ₄ as a protective layer with a thickness of 700 Å.

Next, the substrate on which the above film formation was completed was bonded to a polycarbonate bonding substrate using a hot mel and an adhesive to prepare a magneto-optical disk. This magneto-optical disk was set in a recording / playback device and a bias magnetic field of 200 Oe
While applying the initializing magnetic field of KOe, at a linear velocity of about 8 mm / sec.
A laser beam with a wavelength of 830 nm focused to about 1.5 μm,
3.8mW while modulating at 2MHz with 50% duty
Recording was performed with a binary laser power of 6.4 mW. After that, when reproduction was performed by irradiating a laser beam of 1 mW, a binary signal could be reproduced.

Next, after performing the above experiment, recording was performed on the same track at 3 MHz with the same power. As a result, it was confirmed that the previously recorded signal component was not detected and overwriting was possible.

In this disc, the laser intensity is modulated to "low" and "high" respectively in response to "1" and "0" of the recording signal, and the recording of the present invention (corresponding to claim 2 is performed in the recording magnetic domain). Recording was performed so that the direction of magnetization and the direction of magnetization in the initialization layer are anti-parallel to each other after initialization), then stored for 100 hours in an environment of temperature 70 ° C, initialization magnetic field 2KOe. There was no.

[Comparative Example 1] Instead of recording according to the present invention, recording was performed on the disc of Example 1 by modulating the laser intensities of "high" and "low" respectively in response to recording signals "1" and "0". After performing the temperature 70
When stored for 100 hours in an environment with an initializing magnetic field of 2KOe at ℃, the recorded information changed.

[Example 2] As an initializing layer, a sputtering rate of 10 from the third target was used.
Gd-Tb-Fe-Co alloy is sputtered at 0Å / min., Sputter pressure 1.5 × 10 ^-1 Pa, film thickness 700 Å, T _H = about 220 ° C, H _L = about 5KOe
Except that the Fe-Co sublattice magnetization dominant initializing layer of
A magneto-optical disk similar to that of the example was manufactured and the same experiment was conducted.

As a result, it was confirmed that overwriting was possible.

Recording of the present invention (recording included in claim 1) is performed by modulating the laser intensity to "low" and "high", respectively, corresponding to "1" and "0" of a recording signal on this disc. After that, it was stored in an environment of a temperature of 50 ° C. and an initializing magnetic field of 2 KOe for 100 hours, but the recorded information did not change.

[Comparative Example 2] Instead of recording according to the present invention, recording was performed on the disc of Example 2 by modulating the laser intensities of "high" and "low" corresponding to the recording signals "1" and "0", respectively. Temperature after 50
When stored for 100 hours in an environment with an initializing magnetic field of 2KOe at ℃, the recorded information changed.

The states of magnetization after recording in Examples 1 and 2 and Comparative Examples 1 and 2 are shown in order in FIGS. 3 to 6.

〔The invention's effect〕

As described in detail above, an exchange-coupled two-layer structure including a recording layer having a low Curie temperature and a high coercive force and an initialization layer having a relatively high Curie temperature and a low coercive force as compared with the recording layer is used. Magnetization of the initialization layer is initialized in one direction after irradiating a relatively low laser power corresponding to “1” to a magneto-optical recording medium having a layered perpendicular magnetization film on the substrate. To form a magnetization state in which no interface domain wall exists between the recording layer and the initialization layer, or
After irradiating a relatively high laser power corresponding to “0”, the magnetization of the initialization layer is initialized in one direction, so that the magnetic state in which the interface domain wall exists between the recording layer and the initialization layer is changed. The formation improves the stability of the recording magnetic domain in the overwritable recording method.

[Brief description of drawings]

FIG. 1 is a diagram showing a recording state according to a recording method of the present invention, FIG. 2 is a diagram showing a recording state according to a conventional overwritable recording method, and FIGS. 2 is a diagram showing a state of magnetization after recording in 2 and Comparative Examples 3 and 4. FIG. 1: recording layer, 2: initialization layer, 3: cylindrical domain, 4: Bloch domain wall, 5: interface domain wall, 6: initialization magnetic field.

Claims (2)

[Claims] 1. An exchange-coupled two-layer structure comprising a recording layer having a low Curie temperature and a high coercive force and an initialization layer having a relatively high Curie temperature and a low coercive force as compared with the recording layer. A magneto-optical recording method for performing overwriting by irradiating a magneto-optical recording medium having a perpendicularly magnetized film on a substrate with a laser whose intensity is modulated corresponding to binary information of "1" and "0". In step 1, after irradiating a relatively low laser power corresponding to “1”, the magnetization of the initialization layer is initialized in one direction so that an interface domain wall is formed between the recording layer and the initialization layer. Forming a non-existing magnetization state, and irradiating a relatively high laser power corresponding to “0”, and then initializing the magnetization of the initializing layer in one direction to thereby initialize the recording layer and the initializing layer. Form a magnetization state in which an interface domain wall exists between the layer Magneto-optical recording method characterized by comprising a floor, a. 2. The magneto-optical recording method according to claim 1, wherein the recording layer and the initialization layer are formed of a rare earth-iron group amorphous alloy thin film having a composition opposite to a compensating composition.